This invention relates to cathode ray tubes and, more particularly, to methods and structure for resisting implosion within cathode ray tubes.
Cathode ray tubes being relatively large evacuated glass envelopes are subject to implosion when cracked or fractured. Implosion of such tubes can result in scattering of chucks and splinters of glass.
In recent years, advances in implosion restraint have employed tension bands about certain critical portions of the envelope as fracture restraining means to provide the implosion protection. Color envelopes include a panel joined to a funnel member by ceramic frit, while monochrome envelopes are usually flame sealed together. It has been known for some time that if cracks can be contained in the face of the tube, the tube envelope will devacuate safely rather than implode. The prior art suggests a number of techniques for enhancing the resistance to fracture of cathode ray tube envelopes.
One technique disclosed in U.S. Pat. No. 4,169,274 provides for a pair of substantially U-shaped flat rimbands, each having a reinforcing ridge, encircling the skirt portion of the face plate member, with a forward edge intermediate the mold line and jointure of the skirt. and the window portion. A tension strap is applied intermediate the forward edge and the reinforcing ridge of the rimbands. This approach also discloses, underlying the rimbands, the use of a fiber reinforced tape member with a single adhesive surface in contact with the glass envelope.
Another technique disclosed in U.S. Pat. No. 3,456,076 provides a single tension band about the skirt of the face plate panel with an adhesive tape member having a single adhesive surface in contact with the skirt of the face plate underlying the tension band. Compressive forces are applied to the skirt and tape member to reduce implosion danger of the tube envelope. According to this approach, a variety of adhesive tapes can be utilized, the longitudinal strength of the tape being reinforced by compressive forces of the tension band.
Yet another technique disclosed in U.S. Pat. No. 3,845,530 utilizes a pair of metal rim plates contoured to encircle a tube with the inner surface thereof carrying a non-tacky coating of a tackifiable adhesive. The adhesive is tackified just prior to assembly and caused to adhere to the glass through curing and pressure.
Yet a further technique disclosed in U.S. Pat. No. 3,220,593 utilizes one or more annular bands placed around the tube envelope in the non-viewing perimetrical region of the tube face plate at its substantially maximum exterior cross-sectional dimensions. In using this approach, a hard adhesive such as synthetic or epoxy resin is employed to form a cured and hardened bond between the band or bands and the glass tube.